1. Field of the Invention
The present invention relates to radar devices.
2. Description of the Related Art
There are various radar devices which are widely used in various applications, for example, a motor vehicle field. Such a radar device emits radio waves from a transmitting antenna and receives echoes (reflected radar waves) reflected by objects as detection targets through a receiving antenna array. There is a front running vehicle as a front object as a detection target. Such a conventional radar device detects a distance between an own motor vehicle equipped with the radar device and an object on the basis of a time difference (delay) between a time of transmitting a radio wave and an arrival time of each echo. The radar device further estimates a relative speed between the own motor vehicle and the front object on the basis of a difference in frequency between the received arrival echo and the transmitted radio wave. Japanese patent laid open publication No. 2010-032314 discloses such a conventional radar device. For example, such a conventional radar device is mounted on a motor vehicle and a control unit executes a vehicle driving control on the basis of the arrival echoes of radio waves which are reflected by the front objects.
One of other known radar devices detects the presence of objects on the basis of a comparison result between the amplitude of a received signal of an arrival echo and a threshold value. Such a conventional radar device logarithmically amplifies the received signal of the arrival echo (as the radar wave reflected by an object) and subtracts an average value of the received signals of the arrival echo after the logarithmic amplification, before and after the currently received signal, from the currently received signal in order to suppress a probability of suppressing an incorrect detection of the presence of the object caused by clutter. Such a conventional radar device is disclosed in a technical document, “RADAR SIGNAL PROCESSING TECHNOLOGY”, Matsuo Sekine, pp. 96-103, September 1991, “The Institute of Electronics, Information and Communication Engineers (IEICE)”.
By the way, the conventional radar devices can detect a distance between the own motor vehicle equipped with the radar device and a front object, an azimuth of the front object and a relative speed between the own motor vehicle and the front object. However, the conventional radar devices cannot analyze and determine a type of each front object, for example, cannot determine what the detected front object is, for example a stopped motor vehicle, a running motor vehicle, standing human, walking human, a guard rail, or a traffic sign board.
The conventional radar devices only detect whether or not a received radar wave is reflected from a front object or generated by clutters.